A ground crewman stands in front of a South Korean P3 Orion after it returned from the search for missing Malaysia Airlines Flight MH370 in Perth, Australia.

CANBERRA, Australia (AP) — Malaysia's defence minister defended his military's failure to scramble a fighter jet to follow a Malaysian airliner when it veered off course and vanished two months ago, saying it wasn't seen as a hostile object.

Malaysia Airlines Flight 370 became invisible to civilian radar when its transponder stopped transmitting during a flight from Kuala Lumpur to Beijing on March 8. But the plane was tracked by Malaysian military radar after it turned in a westerly direction across Peninsular Malaysia.

In response to criticism that fighter jets should have been scrambled to investigate the then-unidentified flight through Malaysian air space, Defence Minister Hishammuddin Hussein told Four Corners that the plane was deemed commercial and not hostile.

"If you're not going to shoot it down, what's the point of sending it (a fighter) up?" Hishammuddin asked.

a school utility worker mops a mural depicting the missing Malaysia Airlines Flight 370 Tuesday, April 8, 2014 at the Benigno "Ninoy" Aquino High School campus at Makati city east of Manila, Philippines. Photo: AP.

He said had the Boeing 777 been shot down with 239 passengers and crew on board, "I'd be in a worse position, probably."

Delays in confirming the flight's change of direction led to several days of wasted searching for wreckage in the South China Sea along the airliner's original course, before an analysis of satellite data identified the southern Indian Ocean as a more likely crash site.

Hishammudin previously defended the military's inaction in pursuing the plane for identification after a preliminary report on its disappearance was released early this month.

On that occasion, he said he was informed of the military radar detection two hours later and relayed it to Malaysian Prime Minister Najib Razak, who immediately ordered a search in the Strait of Malacca.

Also on Four Corners, Asuad Khan, the brother-in-law of missing pilot Zaharie Ahmad Shah, rejected speculation that Zaharie was the perpetrator of a mass murder-suicide.

Asuad said media reports that his sister Faizah and her children had left Zaharie hours before the flight were false.

Separately, officials said a Chinese navy survey ship will start mapping the seabed off the west Australian coast this week as part of a new phase of the search.

Chinese, Australian and Malaysian authorities met at the west coast port city of Fremantle over the weekend and agreed that the Chinese ship Zhu Kezhen will conduct a bathymetric survey of the Indian Ocean floor as directed by Australian air crash investigators, Australia's Joint Agency Coordination Centre said in a statement.

The Canberra-based centre said the ship was scheduled to sail for the survey area on Wednesday, weather permitting.

After an initial air and seabed search failed to find any trace of the plane, authorities this month announced a new phase of the search would be conducted over a vastly expanded area of seabed measuring 60,000 square kilometres. The new phase also involves mapping the seabed, where depths and topography are often unknown.

Relatives of Chinese passengers onboard the missing Malaysia Airlines Flight 370 listen, as part of the audio communications between Flight 370's cockpit and air traffic controllers is played, during a meeting with Malaysian officials at a hotel in Beijing. Photo: AP.

Negotiations are underway to contract powerful sonar equipment to scour the seabed for wreckage that could be in water more than seven kilometres deep.

The original search of less than 400 square kilometres of ocean floor where sounds consistent with aircraft black boxes were thought to have emanated was conducted by an unmanned US Navy sub, the Bluefin 21, near its 4.5-kilometre depth limit.

The Bluefin 21 continued searching an ever widening area until a communications problem was discovered last week involving the transponders on the sub and the Australian navy ship that tows it, Ocean Shield.

The centre said the Ocean Shield arrived on Sunday at the Australian west coast port of Geraldton, where preparations are underway to install spare transponder parts on both the ship and sub.

MH370 may have been shot down by mistake during military operation: book

A new book has published accusations that the missing Malaysia Airlines Flight MH370 may have been accidentally shot out of the sky by US and Thai fighter jets in a training exercise mishap.

Flight MH370: The Mystery alleges that a US-Thai joint strike fighter jet training drill shot down the doomed passenger jet and its 239 on board, claiming the search party was intentionally sent in the wrong direction as part of a sophisticated cover-up.

Author Nigel Cawthorne describes how a man, working on an oil rig at the same time the plane's transponders went off, saw a burning jet near the military exercise being conducted.

"After all, no wreckage has been found in the South Indian Ocean, which in itself is suspicious."

He says the hundreds of families of victims will "almost certainly" never know what really happened in the early huors of March 8, 2014.

"Did they die painlessly, unaware of their fate? Or did they die in terror in a flaming wreck, crashing from the sky in the hands of a madman?"

The family of missing Brisbane man Rod Burrows has criticised the timing of the new book's release, saying they are still at pains after 71 days of ongoing search efforts to no avail.

Shares in Malaysian Airlines fell sharply for a second day to hit a record low on Monday, raising pressure on the state-run carrier to come up with a plan to restore investor confidence after missing flight MH370 and widening losses.

Malaysian Airline System Bhd (MAS) last week reported its worst quarterly loss in over two years. Investors were also spooked after the Wall Street Journal on Friday quoted Prime Minister Najib Razak as saying the government could not rule out bankruptcy for the airline.

An official at Najib's office said the comment was from an interview that took place in April, well before the airline's quarterly results were released last Thursday.

Asked about the Wall Street Journal report, a government spokesperson said that Najib had not mentioned bankruptcy specifically but had said the airline's status as a public company needed to be taken into consideration.

According to the government spokesperson, Najib was asked, "Bankruptcy has been mentioned in some quarters as a solution to Malaysia Airlines' problems. What's your view of that?"

And Najib responded: "Well different modalities have been suggested. But we have to look at it from all angles, bearing in mind that MAS is a government-linked company. It’s not a private company so there are certain repercussions in what you want to do in terms of how it is being received by the employees and the general public."

Shares in Malaysian Airlines fell as much as 21 percent to a low of 15 sen, equivalent to just 5 U.S. cents, in heavy trade on Monday morning, adding to a drop of 9.5 percent on Friday. By late afternoon the stock was trading at 15.5 sen, a drop on the day of 18.4 percent.

The airline's market value has plunged about 50 percent so far this year.

"It's a bit drastic what's happening to the stock, but I think it will struggle to make profit in the next year or two years and investors are cashing out now," said Jerry Lee, an analyst with RHB Investment Bank.

The airline said on Thursday the impact of the disappearance in March of flight MH370 had pushed it to its worst quarter in over two years, with a sharp drop in passenger traffic likely preventing it from returning to profit this year.